Forgive my terminology. Is it acceptable to replace one of the large breakers (fuse) for one of the smaller dual breakers if I need to expand my fuse box for additional wiring. Is this something considered ok for a long term need. thanks.

Thats what they make them for, and it good for long term. Just ask for
piggy back breakers. The only thing you have to watch is, don't over amp
your service or you will be snapping off your main breaker. Later Paul